Increasingly, copyrightable content is being distributed in digital form on various physical media types, including Digital Versatile Disk (DVD). While digital content, such as video and music, has provided greater fidelity to the consumer, it has the significant drawback of being relatively easy to reproduce perfect copies of the content without the authorization of the copyright owner. Analog content is also susceptible to illicit reproduction and/or use. Because analog and/or digital content may be copied at any point along the path through which it is transmitted, a number of security measures are usually utilized in combination.
A variety of techniques are available for protecting analog and/or digital content stored in a storage medium from unauthorized copying such as scrambling and encryption/decryption techniques.
However, the integrity of some copy protection techniques has been compromised and such copy protection techniques are no longer technically effective against unauthorized copying of copyrighted material. For example, in digital versatile disc (DVD) technology, the integrity of content scramble system (CSS) for scrambling DVD video contents has been recently compromised by hackers. Software programs are now available that can descramble the contents of CSS-protected DVDs. Thus, unauthorized parties may be able to copy and/or play back decrypted digital content.
Additionally, content on a storage medium is usually transmitted from a source, drive, or storage device (i.e. any device capable of accessing data from a storage medium) to a destination or host device (i.e. any device capable of retrieving data from the source or storage device) over a data bus in a form that can be captured by anyone having the proper equipment. Although the data transmitted may not be in its original form (i.e. content may be encrypted and/or scrambled), a copy of the encrypted and/or scrambled data captured at the time of the transmission may still be playable by presenting the encrypted data to a host device as though it was coming from a legitimate storage device.
Another situation in which analog and/or digital content (copyright protected or otherwise) may be compromised is when it is transmitted across an interface (i.e. from a source device to a destination device, etc.) in analog form which can be easily copied and reproduced. In this instance, the content may be unencrypted and/or unscrambled making it possible to create unprotected copies of the content.
One security measure for protecting content against unauthorized use and/or copying employs watermarking as a part of the protection scheme. Watermarking is a technique by which information is embedded into content in such a way that it is transparent to users of the content, is difficult to remove from the content, and can be robustly detected in the content by specialized hardware or software.
In some systems, the watermark may indicate conditions and requirements constraining use of the content, including constraints specific to copying. In various devices, the watermark serves to control/restrict use, access, playback, and/or reproduction of the content.
A recording device that is compliant with a watermarking system may be required to detect the watermark in content that is to be copied, particularly when such content is received in unprotected or unencrypted form. If a watermark is present, the device only makes a copy if permitted by the watermark. When making an authorized copy of watermarked content, the compliant recording device may also be required to update the watermark to reflect the copy, and encrypt the copy in the case of certain types of storage media.
A player, host, or source device that is compliant with a watermark protection system may be required to detect the watermark in content that is to be played back from a storage medium, particularly when such content is stored in unprotected or unencrypted form. If a watermark is present, the player device prevents such playback in cases where the watermark's state is inconsistent with the requirements indicated by the watermark. For example, playback might be prevented in cases where watermarked content is found unencrypted on a storage medium for which it should have been encrypted. As another example, playback might be prevented for a copy of content that contains a watermark that either (1) was not properly updated to reflect the copy, or (2) indicates that the copy was not authorized.
Watermarks may be employed in conjunction with, or independent of, other content protection systems such as encryption and/or scramble content protection. For example, encryption may be required for watermarked content distributed on pre-recorded storage media. In another example, the watermarks may be employed with unprotected or unencrypted content. This may be the case where (1) the content was originally stored without encryption or (2) the content has been decrypted and copied without authorization.
Despite the added content protection provided by the use of watermarks, the location of the watermark detector may result in compromising the content being protected. Depending on how the watermark is detected and processed, the content may be susceptible to unauthorized copying.